We report the synthesis and biological properties of three modified dinucleotides T*G, G*T and T*T in winch the natural phosphodiester linkage has been replaced by a methylene carboxamide unit. They have been designed to act as nucleomimetics of a sequence recognized by the HIV-1 nucleocapsid protein NCp7 and to inhibit this interaction. (C) 1999 Elsevier Science Ltd. All rights reserved.